public class Tractors {
    double load;
    double volume;

    public Tractors(double load,double volume){
        this.load=load;
        this.volume=volume;
    }
    public String start(){
     return "拖拉机在农田里缓慢启动";
    }
    public String speed(){
        return "拖拉机开始加速了";
    }
}
